1. Field of the Invention
The present invention relates to a gas turbine engine combustor having at least one trapped vortex cavity and, more particularly, to an apparatus and method for injecting fuel into such cavity and providing high inlet air flows to the combustion chamber through flow passages of a dome inlet module in accordance with a Rich-Quench-Lean (RQL) process.
2. Description of Related Art
Advanced aircraft gas turbine engine technology requirements are driving the combustors therein to be shorter in length, have higher performance levels over wider operating ranges, and produce lower exhaust pollutant emission levels. One example of a combustor designed to achieve these objectives is disclosed in U.S. Pat. No. 5,619,855 to Burrus. As seen therein, the Burrus combustor is also to operate efficiently at inlet air flows having a high subsonic Mach Number. This stems in part from a dome inlet module which allows air to flow freely from an upstream compressor to the combustion chamber, with fuel being injected into the flow passage. The combustor also has inner and outer liners attached to the dome inlet module which include upstream cavity portions for creating a trapped vortex of fuel and air therein, as well as downstream portions extending to the turbine nozzle.
It will be noted in the aforementioned Burrus combustor that the fuel is injected into the trapped vortex cavities through a portion of the liner forming an aft wall of such cavity. Fuel is also injected into the flow passages of the dome inlet module via atomizers located along hollow vanes of the dome inlet module, the vanes being in flow communication with a fuel manifold. While functional for its intended purpose, it has been found that the fuel injection approach taken in the '855 patent lacks simplicity. In particular, it will be understood that this design requires the occupation of significant space within the combustor housing cavity, as separate systems are utilized for injecting the fuel into the cavities and the dome inlet module. This not only represents a large cost from a manufacturing standpoint, but extraction of fuel injectors from the engine for repair or replacement with a major tear down of the engine to expose the combustor cavity section is not permitted.
In order to address the concerns associated with the '855 combustor, a new design employing a plurality of circumferentially spaced fuel injector bars are located upstream of a modified dome inlet module is shown and disclosed in a patent application Ser. No. 09/215,863 entitled "Fuel Injector Bar For A Gas Turbine Engine Combustor Having Trapped Vortex Cavity," which is also owned by the assignee of the present invention, hereby incorporated by reference, and filed concurrently herewith. It will be appreciated that the combustor of this concurrently filed patent application utilizes the fuel injector bars to inject fuel into the cavities in the liner, as well as the flow passages of the dome inlet module in a dual stage process.
Another method for achieving low emissions within combustor designs is a concept known as Rich-Quench-Lean (RQL). This concept features a very rich primary combustion zone with local equivalence ratios typically much greater than 1.0, which allows initiation of the mixing of the fuel with some of the combustor air and provides combustion under oxygen deprived conditions. Accordingly, formation of nitrous oxide (NOx) in the primary zone is reduced. The partially burned combustion gases from the rich primary zone then undergo a rapid dilution from the injection of significant amounts of additional fresh combustor air. The difficulty is in achieving a rapid mixing of the fresh air with the rich primary zone combustion gases to drive the overall mixture quickly to a lean state (i.e., an equivalence ratio well below 1.0). This prevents NOx formation in the dilution zone by not allowing the combustion gases sufficient time at local equivalence ratios between 0.85 and 1.15 where rapid NOx formation occurs. While RQL combustors have a significant advantage over other low emissions concepts in the area of combustion dynamics, it is known that low emissions, good combustion efficiency, and good exit gas temperature profile and pattern are difficult to achieve in the RQL concept.
Accordingly, it would be desirable for a combustor design to be developed which is compatible with use of the RQL concept. It would also be desirable for a fuel injection system to be developed in a gas turbine engine combustor having a liner with one or more trapped vortex cavities so that the RQL concept can be utilized therewith.